This invention relates to stimulation procedures to increase oil recovery.
The use of aqueous acidic compositions for treating subterranean formations to stimulate the production of hydrocarbons therefrom by acidizing and/or fracturing is known. It is also known to thicken such aqueous acid compositions by incorporating a water soluble or water dispersible polymeric viscosifier. Various gelling or crosslinking agents and/or foaming agents have been added to polymer-containing aqueous acid compositions to form retarded acid gels suitable for introduction into subterranean formations. However, the polymeric thickening agents are degraded by hostile reservoir environments such as high temperature, acidity and shear conditions as well as electrolytes encountered in acidizing processes. These stimulation techniques which last only a few days at most (after which the well returns to normal, but enhanced, production) distinguishes from enhanced oil recovery techniques which involve injection of polymers which remain in use for months.